diff --git a/cmake/modules/HandleLLVMOptions.cmake b/cmake/modules/HandleLLVMOptions.cmake
index 0b1e51ba0a..8520fed06b 100644
--- a/cmake/modules/HandleLLVMOptions.cmake
+++ b/cmake/modules/HandleLLVMOptions.cmake
@@ -531,6 +531,13 @@ if (UNIX AND
   append("-fcolor-diagnostics" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 endif()
 
+# HLSL Change Starts
+# Enable -fms-extensions for clang to use MS uuid extensions for COM.
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+  append("-fms-extensions -Wno-language-extension-token" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+endif()
+# HLSL Change Ends
+
 # Add flags for add_dead_strip().
 # FIXME: With MSVS, consider compiling with /Gy and linking with /OPT:REF?
 # But MinSizeRel seems to add that automatically, so maybe disable these
diff --git a/include/dxc/Support/WinAdapter.h b/include/dxc/Support/WinAdapter.h
index 0f394347cb..b028992446 100644
--- a/include/dxc/Support/WinAdapter.h
+++ b/include/dxc/Support/WinAdapter.h
@@ -46,16 +46,33 @@
 #define CoTaskMemFree free
 
 #define SysFreeString free
-#define SysAllocStringLen(ptr, size) (wchar_t*)realloc(ptr, (size + 1)*sizeof(wchar_t))
+#define SysAllocStringLen(ptr, size)                                           \
+  (wchar_t *)realloc(ptr, (size + 1) * sizeof(wchar_t))
 
 #define ARRAYSIZE(array) (sizeof(array) / sizeof(array[0]))
 
 #define _countof(a) (sizeof(a) / sizeof(*(a)))
 
+// If it is GCC, there is no UUID support and we must emulate it.
+#ifdef __APPLE__
+#define __EMULATE_UUID 1
+#else // __APPLE__
+#ifdef __GNUC__
+#ifndef __clang__
+#define __EMULATE_UUID 1
+#endif // __GNUC__
+#endif // __clang__
+#endif // __APPLE__
+
+#ifdef __EMULATE_UUID
 #define __declspec(x)
+#endif // __EMULATE_UUID
+
 #define DECLSPEC_SELECTANY
 
+#ifdef __EMULATE_UUID
 #define uuid(id)
+#endif // __EMULATE_UUID
 
 #define STDMETHODCALLTYPE
 #define STDAPI extern "C" HRESULT STDAPICALLTYPE
@@ -188,7 +205,8 @@
 #define OutputDebugStringA(msg) fputs(msg, stderr)
 #define OutputDebugFormatA(...) fprintf(stderr, __VA_ARGS__)
 
-#define CaptureStackBackTrace(FramesToSkip, FramesToCapture, BackTrace, BackTraceHash)\
+#define CaptureStackBackTrace(FramesToSkip, FramesToCapture, BackTrace,        \
+                              BackTraceHash)                                   \
   backtrace(BackTrace, FramesToCapture)
 
 // Event Tracing for Windows (ETW) provides application programmers the ability
@@ -413,19 +431,55 @@ typedef void *HMODULE;
 
 //===--------------------- ID Types and Macros for COM --------------------===//
 
-struct GUID {
+#ifdef __EMULATE_UUID
+struct GUID
+#else  // __EMULATE_UUID
+// These specific definitions are required by clang -fms-extensions.
+typedef struct _GUID
+#endif // __EMULATE_UUID
+{
   uint32_t Data1;
   uint16_t Data2;
   uint16_t Data3;
   uint8_t Data4[8];
-};
+}
+#ifdef __EMULATE_UUID
+;
+#else  // __EMULATE_UUID
+GUID;
+#endif // __EMULATE_UUID
 typedef GUID CLSID;
 typedef const GUID &REFGUID;
-typedef const void *REFIID;
 typedef const GUID &REFCLSID;
 
+#ifdef __EMULATE_UUID
+typedef const void *REFIID;
 #define IsEqualIID(a, b) a == b
 #define IsEqualCLSID(a, b) !memcmp(&a, &b, sizeof(GUID))
+#else  // __EMULATE_UUID
+typedef GUID IID;
+typedef IID *LPIID;
+typedef const IID &REFIID;
+inline bool IsEqualGUID(REFGUID rguid1, REFGUID rguid2) {
+  return !memcmp(&rguid1, &rguid2, sizeof(GUID));
+}
+
+inline bool operator==(REFGUID guidOne, REFGUID guidOther) {
+  return !!IsEqualGUID(guidOne, guidOther);
+}
+
+inline bool operator!=(REFGUID guidOne, REFGUID guidOther) {
+  return !(guidOne == guidOther);
+}
+
+inline bool IsEqualIID(REFIID riid1, REFIID riid2) {
+  return IsEqualGUID(riid1, riid2);
+}
+
+inline bool IsEqualCLSID(REFCLSID rclsid1, REFCLSID rclsid2) {
+  return IsEqualGUID(rclsid1, rclsid2);
+}
+#endif // __EMULATE_UUID
 
 //===--------------------- Struct Types -----------------------------------===//
 
@@ -503,22 +557,37 @@ enum tagSTATFLAG {
 
 //===--------------------- UUID Related Macros ----------------------------===//
 
+#ifdef __EMULATE_UUID
+
 // The following macros are defined to facilitate the lack of 'uuid' on Linux.
 #define DECLARE_CROSS_PLATFORM_UUIDOF(T)                                       \
 public:                                                                        \
   static REFIID uuidof() { return static_cast<REFIID>(&T##_ID); }              \
                                                                                \
 private:                                                                       \
-   __attribute__ ((visibility ("default"))) static const char T##_ID;
+  __attribute__((visibility("default"))) static const char T##_ID;
 
-#define DEFINE_CROSS_PLATFORM_UUIDOF(T) __attribute__ ((visibility ("default"))) const char T::T##_ID = '\0';
+#define DEFINE_CROSS_PLATFORM_UUIDOF(T)                                        \
+  __attribute__((visibility("default"))) const char T::T##_ID = '\0';
 #define __uuidof(T) T::uuidof()
 #define IID_PPV_ARGS(ppType)                                                   \
   (**(ppType)).uuidof(), reinterpret_cast<void **>(ppType)
 
+#else // __EMULATE_UUID
+
+#define DECLARE_CROSS_PLATFORM_UUIDOF(T)
+#define DEFINE_CROSS_PLATFORM_UUIDOF(T)
+
+template <typename T> inline void **IID_PPV_ARGS_Helper(T **pp) {
+  return reinterpret_cast<void **>(pp);
+}
+#define IID_PPV_ARGS(ppType) __uuidof(**(ppType)), IID_PPV_ARGS_Helper(ppType)
+
+#endif // __EMULATE_UUID
+
 //===--------------------- COM Interfaces ---------------------------------===//
 
-struct IUnknown {
+struct __declspec(uuid("00000000-0000-0000-C000-000000000046")) IUnknown {
   virtual HRESULT QueryInterface(REFIID riid, void **ppvObject) = 0;
   virtual ULONG AddRef();
   virtual ULONG Release();
@@ -533,25 +602,29 @@ struct IUnknown {
   DECLARE_CROSS_PLATFORM_UUIDOF(IUnknown)
 };
 
-struct INoMarshal : public IUnknown {
+struct __declspec(uuid("ECC8691B-C1DB-4DC0-855E-65F6C551AF49")) INoMarshal
+    : public IUnknown {
   DECLARE_CROSS_PLATFORM_UUIDOF(INoMarshal)
 };
 
-struct IMalloc : public IUnknown {
+struct __declspec(uuid("00000002-0000-0000-C000-000000000046")) IMalloc
+    : public IUnknown {
   virtual void *Alloc(size_t size);
   virtual void *Realloc(void *ptr, size_t size);
   virtual void Free(void *ptr);
   virtual HRESULT QueryInterface(REFIID riid, void **ppvObject);
 };
 
-struct ISequentialStream : public IUnknown {
+struct __declspec(uuid("0C733A30-2A1C-11CE-ADE5-00AA0044773D"))
+    ISequentialStream : public IUnknown {
   virtual HRESULT Read(void *pv, ULONG cb, ULONG *pcbRead) = 0;
   virtual HRESULT Write(const void *pv, ULONG cb, ULONG *pcbWritten) = 0;
 
   DECLARE_CROSS_PLATFORM_UUIDOF(ISequentialStream)
 };
 
-struct IStream : public ISequentialStream {
+struct __declspec(uuid("0000000c-0000-0000-C000-000000000046")) IStream
+    : public ISequentialStream {
   virtual HRESULT Seek(LARGE_INTEGER dlibMove, DWORD dwOrigin,
                        ULARGE_INTEGER *plibNewPosition) = 0;
   virtual HRESULT SetSize(ULARGE_INTEGER libNewSize) = 0;